Nitrocellulose grain having crosslinked polymeric deterrent coating and process of making

ABSTRACT

CROSSLINKED POLYMERIC DETERRENT COATINGS FOR PROPELLANT GRAINS FOR REDUCING THE BURNING RATE OF OUTER PORTIONS OF THE GRAINS, AND COMPRISING COMPOSITIONS, TYPICALLY, OF RESINS OF POLYVINYL BUTYRAL AND MELAMINE FORMALDEHYDE; SOLVENTS OF ETHYL ALCOHOL, METHYLENE CHLORIDE AND   CCL2-CCLF2   AND A CATALYST SUCH AS TRIFLUORACETIC ACID, THE DETERRENT COMPOSITION CROSSLINKING UPON CURING AT 50-60*C. FOR A PERIOD OF ABOUT 5-24 HOURS.

3,582,726 Patented Aug. 8, 1972 3,682,726 NITROCELLULOSE GRAIN HAVING CROSS- LINKED POLYMERIC DETERRENT COAT- ING AND PROCESS OF MAKING Ludwig Stiefel, Philadelphia, Pa., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Apr. 29, 1969, Ser. No. 820,711

Int. Cl. C061) 19/02 US. Cl. 149-10 11 Claims ABSTRACT OF THE DISCLOSURE STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes Without the payment to me of any royalties thereon.

BACKGROUND OF THE INVENTION This invention relates to propellants and more particularly concerns solid propellants which are coated with an improved deterrent for reducing the burning rate of outer portions of the propellant grains.

As is generally known in the art, deterrents aid in permitting the attainment of a given projectile velocity with a peak pressure lower than that encountered when deterrents are not used. Currently, deterrents such as dinitrotoluene, dibutyl phthalate and ethyl centralite are being used. Their application to propellants consists essentially of slurrying the propellants in water, the abovementioned deterrent then being added to the water in the form of an emulsion. Heating the resultant slurry causes the deterrent to penetrate the nitrocellulose of the propellant grain.

Upon elevated temperature storage this type ofdeterrent can migrate further into the grains resulting in detrimental changes of the ballistic properties of .the propellant from accepted standards.

If a propellant grain includes a water soluble constitucrystalline material, prior art methods would not permit adequate absorption of the deterrent into the propellant matrices. My deterrent need only coat the outer surfaces of the grains.

My crosslinked deterrents offer other advantages. Since crosslinking fixes the deterrent on the propellant surfaces only, performance characteristics of the propellant will tend to be more stable even after long term storage at elevated temperatures. Crosslinking also improves thermal stability of the coating and renders the coating solvent resistant. Thus, varying thicknesses of the deterrent may readily be applied to the propellant grains, since, after curing of the deterrent on the grains, the cured coating already deposited will not be softened by the solvent of subsequent coats.

Another important advantage of my deterrent coating resides in its ability to crosslink after curing for several hours at a relatively low temperature of about 55 C.,

which is quite compatible for small arms propellant grains. It is therefore an object of the present invention to provide improved deterrents for propellants grains.

Another object of the invention is to provide deterrents for solid propellants which form crosslinked polymers at relatively low temperatures.

Still another object of the invention is to provide deterrent compositions for those solid propellants having water soluble constituents which would normally be leached therefrom when conventional water slurry methods are employed.

' Yet another object of the invention is to provide deterrent compositions which need not be absorbed into the propellant matrices but only on surfaces thereof for subsequent curing of the deterrent into crosslinked polymers.

A still further object of the invention is to provide deterrent compositions which can readily be coated in varying thicknesses on solid propellant grains, the coating having good shelf life even when the propellant grains are subjected to elevated temperatures for extended periods.

These and further objects of the invention will in part be obvious and in part appear hereinafter in the following description.

A preferred example of my deterrent composition is shown below:

TABLE I.CROSSLINKED POLYMER DETERRENT l B.P. 47.6" C.

. While polyvinyl butyral has been found to be an ex cellent carrier resin for the purpose hereinabove described, other compatible film forming resins such as acrylics, for example n-butyl methacrylate and methyl methacrylate; and cellulose, ethyl cellulose and hydroxy ethyl cellulose.

If the upper limit of 10 weight percent of polyvinyl butyral is used, the deterrent will possess high adhesive and flexibility characteristics. Conversely, if the upper limit of the melamine formaldehyde is used, the deterrent Will be less flexible and hard. Other formaldehyde type resins can be used advantageously, such, for example, as triazinev formaldehyde and alkylated melamine formaldehyde, in the same amounts as listed in the table above.

Similarly, the solvents may be combined. Viscosity, volatility and flammability requirements dictate the amount of solvent needed. A high proportion of halogenated solvents will be used if flammability hazards are desired to be reduced. Other halogenated solvents such as an azeotrope of ethyl alcohol and CCl F--CCl(F B.P. 44.6 (3.; 65% CCl2F-CCIF2 and 35 ethyl alcohol, B.P.- 483 C.; 65% CCl F-CClF and 35% isopropanol, B.P. 48.9 C.; an azeotrope of CChF-CClF and methylene chloride, B.P. 47.6 C.; CCl F, B.P. 137.4" C.; and CCl FCCl F, B.P. 203.8 C., may be substituted for the CCl FCClF solvent used in Table I.

Volatility of the liquid deterrent may be lowered by substituting higher molecular weight alcohols such as propyl or butyl alcohols for the ethyl alcohol. The alcohol and methylene chloride may be present in my deterrent solution in order that the resins may be dissolved.

Trifluoro-acetic acid may be replaced with p-toluene sulfonic acid or methane sulfonic acid in amounts specified in the table for the catalyst.

The amount of coating to be applied to any suitable propellant grain will depend on the particular ballistics desired, the granulation of the propellant, and the ignition and combustion behavior of the particular coating formulation.

curing said coated grains to crosslink said polymeric deterrent on the grain surfaces.

2. The method of claim 1 wherein said polyvinyl butyral is present in an amount ranging between about to weight percent, and at least one of said formalde- Although it is not intended that the invention be hmhyde resins being present in an amount ranging between ited thereto, there is set forth hereinbelow for purposes about 5 to .15 weight percent. of illustration, examples of my crosslinked deterrent 3. The method of claim 1 wherein said alcohols are compositions:

EXAMPLE I Cure Tem-

,. pere- Propellant grain, Deterrent composition, ture, weight percent Grain shape weight percent C. Hour Polyvinyl butyral, 7.9. D Melamine formaldehyde, 6.0.. Nitrocellulose, 80.0; Spherical- Ethyl alcohol, 72.0- 54 ll nitroglycerine, 10.0; Methylene chloride, 15. diphenylamine, 1.0. Tritluoro-acetic acid, 0.

Method of application: Airless spray-pan coating EXAMPLE II Cure Tempera- Propellant grain, Deterrent composition, ture, weight percent Grain shape weight percent 0. Hours N itrocellnlose, 99.0; Cylindrical, Polyvinyl butyral, 7.0. V

diphenylamine, 1.0. single per- Triazine tormaldehyde 2 9 ioration. Buryl alcohol, 50.0-. 55 2 CClaF-CClFa, 40.0-- p-Toluene sulfonic acid, 0.1--

Method of application: Fluidized bed process EXAMPLE III Cure Tempera- Propellant grain, Deterrent composition, ture, weight percent Grain shape weight percent 0. Hours Polyvinyl butyral, 7.92-..

Melamine iormaldehyde, 2. Ethyl alcohol, 40.00---.

Nitrocellulose, 90.0; Cylind ical,

e. Bugyl alcohol, 40.00

nitrozlycerine, 10.0. singl Methylene chloride, 10.00

Methane ullonic acid, 0.08

Method of application: Fluidized bed process The methods of application are well known processes and will not be herein described.

The crosslinking reaction is caused to take place by curing the newly applied grain for 5 to 24 hours at about -60 C. Y

My coating formulation may incorporate ignitability additives, anti-fouling agents, flash inhibitors, and the like, and I do not wish it to be limited to the exact details as above described, for obvious modifications will occur to a person skilled in the art.

I claim:

l. A method for providing a crosslinked polymeric deterrent coating on solid propellant grains containing nitrocellulose comprising:

making a polymeric deterrent solution of resins and solvents for said resin, and a catalyst, said resins being selected from the group consisting of polyvinyl butyral, melamine formaldehyde, triazine formaldehyde, alkylated melamine formaldehyde, -n-butyl methacrylate, methyl methacrylate, methyl cellulose, ethyl cellulose, and hydroxy ethyl cellulose; said solvents being selected from the group consisting of methylene chloride, alcohols and mixed pe'rhalogenated olefins; said catalyst being selected from the group consisting of trifiuoro-acetic acid, p-toluene sulfonic acid and methane sulfonic acid,

applying said solution to said propellant grains to form a coating thereon, and I selected from the group consisting of ethyl, propyl and butyl.

4. The method of claim 1 wherein said mixed perhalogenated olefins are selected from the group consisting of CCl F-CClF boiling point 47.6 C.; azeotrope of ethyl alcohol and CCl 'FCC1F boiling point 44J6 C.; 65% CClgF--CClF2 and 35% ethyl alcohol, boiling point 48.3 C.; 65% CCI2F-CC1F2 and 35% isopropanol, boiling point 48.'9 C.; azeotrope of CC1=F--CC1F and methyl- 'ene chloride, boiling point 47.6" C.; CCl F, boiling point l37.4 C.; and CCl FCCl F, boiling point 203.8 C.

5. The method of claim 1 wherein said methylene chloride is present in an amount ranging between about 10 to 50 weight percent.

' 6. The method of claim 1 wherein said catalyst is present in an amount ranging between about 0.05 to 0.15 weight percent.

7. The method of claim 6 wherein said alcohols are present in an amount ranging between about 10 to weight percent.

8. The method of claim 7 wherein said mixed perhalogenated olefins are present in trace amounts up to about 60 weight percent.

9. A solid propellant grain and a crosslinked polymeric deterrent coating on said solid propellant grain, said propellant comprising at least 89 weight percent nitrocellulose, the balance of said propellant being selected from the group consisting of 10 weight percent nitroglycerine and 1 weight percent diphenylamine; 1 weight percent diphenylamine; and 10 weight percent nitroglycerine; said deterrent coating being made from a solution of 10 weight percent polyvinyl butyral, 4.9 weight percent melamine formaldehyde, 15 weight percent ethyl alcohol, 15 weight percent methylene chloride, 55 weight percent melamine formaldehyde, n-butyl methacrylate, methyl methacrylate, methyl cellulose, ethyl cellulose, and hydroxy ethyl cellulose.

11. The coating of claim 10 wherein said polyvinyl butyral is present in an amount ranging between about 5 to 10 weight percent, and at least one of said formaldehyde resins being present in an amount ranging between about 5 to 15 weight percent.

References Cited UNITED STATES PATENTS 4/1934 McBride 14911 9/1943 Allison et al. 149|10 CARL D. QUARFORTH, Primary Examiner S. J. LECH'ERT, JR., Assistant Examiner US. Cl. X.R. 149-9, ll, 98, 100 

